In a First-Order Reaction with Only One Reagent, the Reaction

In a first-order reaction with only one reagent, the reaction was started with a concentration of reactant equal to 0.0800 M. After exactly two hours, the concentration had fallen to 0.0400 M. What is the molarity after exactly six hours?

A) 0.0000 M
B) 0.0100 M
C) 0.0150 M
D) 0.0200 M
E) 0.0300 M